While NASA's Curiosity rover found that Mars could have once supported life at some point in the ancient past, scientists still haven't been able to detect a definitive sign that either single cellular or multicellular life once roamed the Red Planet.

"Suppose we landed on Mars and we saw a skyscraper, a huge building 10 stories high or something," NASA Ames Research Center astrobiologist Chris McKay said. "It would be clear that that was not just a pile of rocks even if the building was abandoned. Biologically, there's an equivalent. Things like proteins and DNA and enzymes are the biological equivalent of skyscrapers. They're huge, complex molecules that were assembled for a particular purpose." [The Search for Life on Mars (Photos)]

A sketch of the design for NASA's 2020 Mars rover, which will be based heavily on the agency's Curiosity rover. Agency officials will announce the 2020 rover's science instruments on July 31, 2014.

Credit: NASA/JPL-Caltech

Finding life with a new rover

This shows one prototype for hardware to cache samples of cores drilled from Martian rocks for possible future return to Earth. A major objective for NASA's Mars 2020 rover, as described by the Mars 2020 Science Definition Team, would be to collect and package a carefully selected set of up to 31 samples in a cache that could be returned to Earth by a later mission. For scale, the diameter of the core sample shown in the image is 0.4 inch (1 centimeter).

Scientists aiding in the development of the rover have said that researchers will have a better chance of detecting indicators of past life on Mars than finding microbes today..

"To go and look for simple organisms, or not-so-simple organisms, that are living within that toxic, harsh environment we just think is a foolish investment of the technology at this time," Jack Mustard, a professor at Brown University and chairman of the 2020 rover mission's Science Definition Team told reporters last week in a news conference.

NASA scientists have also recommended that the new rover collect rock samples that can be saved and eventually brought back to Earth on a future mission. Returning samples to Earth will allow scientists to perform advanced experiments with sensitive instruments found in a laboratory.

"That [sample return] would be an enormous step forward in our astrobiological exploration of Mars," Cornell University scientist Alberto Fairen wrote in an email to SPACE.com.

Life already found?

Some scientists contend that signs of life were already found by the first American lander to touchdown on the Red Planet. Viking 1 — which landed on Mars in 1976 — performed a life-detection experiment that many scientists agree did not uncover life.

NASA's Viking probes were the first ever to successfully set footpad on Mars in a powered landing. The Viking 1 lander set down in July 1976 and didn't go silent until November 1982. Viking 2 landed in September 1976 and kept working until April 1980. Credit: NASA

Credit: NASA

Recently, some scientists have expressed doubt about those conclusions. Some contend that it is possible that Viking 1 destroyed the organic matter the spacecraft was designed to detect or that its instruments weren't sensitive enough to find the organics the researchers were looking for.

McKay, however, doesn't think Viking 1 found life. The surface of Mars is too zapped by radiation to preserve organics, McKay said, therefore the Viking sample — gathered from the surface of the planet — would not have played host to any life-affirming material. [The Boldest Mars Missions in History]

"It seems from the results we have from Curiosity and from previous missions and also from laboratory experiments, radiation on the surface of Mars, together with perchlorate is destroying organics down into the subsurface, so we need to get below the level that radiation can reach," about 16.4 feet (5 meters) into the ground, McKay said.

Do you think life exists on Mars today?

Yes - The Red Planet is teeming with tiny microbes, we just haven't found them yet.

Although the instruments on the 2020 rover are expected to seek out signs of ancient life, another instrument currently in development would help search for life signs in the more recent past.

MIT researcher Chris Carr and a team of researchers are currently developing a biomarker-seeking instrument. He is betting that life on Mars is distantly related to life on Earth. The instrument analyzes Martian dirt to uncover genomic information left behind by microorganisms that died out up to 1 million years ago. The tool should be able to detect signatures of DNA and RNA on Mars.

McKay even broadens the scope of Carr's work. Although strands of DNA and RNA are only detectable for about one million years on Earth, Martian genomic information could last much longer because of the cool, dry environment on Mars.

"The sort of processes that destroy evidence of life on Earth over time have not been operating on Mars and so there's a better chance that on Mars we might find something that's a biomarker that's been there for billions of years so the method doesn't necessarily preclude recent or old life," McKay said. "The distinction is not so important on Mars."

No planet is more steeped in myth and misconception than Mars. This quiz will reveal how much you really know about some of the goofiest claims about the red planet.

"If there's life on Mars, it could be related to life on Earth due to meteoritic transfer between the planets, and this would have largely happened on the order of 3 1/2 or more on the order of 4 billion years ago during a period called the Late Heavy Bombardment, when there were many large impact events," Carr told SPACE.com. "These impact events transferred on the order of 1 billion tons of rock between Earth and Mars largely from Mars to Earth."

Any life-detection experiment would need a few safeguards to be sure that Earth microbes don't contaminate a Martian sample.

"Currently, planetary protection allows microbes on the spacecraft," McKay said. "Curiosity is estimated to have flown to Mars with half a million Earth microorganisms on it … but if I was doing a life-detection experiment, those guidelines would not be acceptable."

McKay said he would want hospital-level sterilization for any rover attempting a life detection experiment. The entire robot wouldn't need to be sterilized, however. Only the instruments performing life-detection investigations would need to be rigorously guarded.

Editor's Recommendations

Miriam Kramer joined Space.com as a staff writer in December 2012. Since then, she has floated in weightlessness on a zero-gravity flight, felt the pull of 4-Gs in a trainer aircraft and watched rockets soar into space from Florida and Virginia. She also serves as Space.com's lead space entertainment reporter, and enjoys all aspects of space news, astronomy and commercial spaceflight.

Miriam has also presented space stories during live interviews with Fox News and other TV and radio outlets. She originally hails from Knoxville, Tennessee where she and her family would take trips to dark spots on the outskirts of town to watch meteor showers every year. She loves to travel and one day hopes to see the northern lights in person. You can follow Miriam on Twitter and Google+.